Monthly Tech Tip

Question
We have some rubber parts that have been in inventory for over a year, because we over-ordered. Are these parts still good, or should we replace them? What’s the rule of thumb on rubber part shelf-life?

Answer:
Rubber, if stored in the perfect environment, could last for centuries. However, we don’t live in a perfect world where we have perfect environmental conditions, so we need to look at what environmental conditions can affect the longevity of rubber components.

We should all know that if a rubber component is exposed to gases or liquids will definitely affect the life of rubber components since we test in those conditions to see what will affects the conditions will have on the rubber over time. The ones that have the most affect on storage of rubber components are the ones we don’t see or think off.

There are four main areas that affect rubber in storage. The first is temperature. Depending on the polymer type will regulate how much temperature it takes to start effecting a change in the rubber. Many companies store their rubber parts on shelves in a warehouse, and many time, at one of the higher levels in the rack. Most warehouses are not temperature controlled so the temperature is highest nearest the ceiling of the warehouse. I have seen these temperatures exceed 130ºF. These temperatures will cause aging in materials such as Natural rubber, SBR rubbers, butyl rubbers, nitrile rubbers, polychloroprene rubbers, and others. The ideal temperature to maintain is around 75ºF.

The next two areas I am combining as they are of similar origins. They are oxidation and ozone. Both are naturally occurring and affect the saturated portion of the polymer chain. Many polymers require the addition of antioxidants and antiozonants to retard the effects of these naturally occurring phenomena. Some materials such as EPDM, Silicone, and Fluorocarbon are naturally resistant to these phenomena due to not containing any sites for the oxygen and ozone to attack.

The last is one many people overlook and that is the presence of UV light. UV light can be generated by sunlight and by artificial light. UV can cause damage to the backbone of the polymer reducing the properties of the material. If the rubber component is of non-black formulations, the UV can affect the color and causing a minor to major change in the color. Carbon black filled rubber components are much less susceptible to UV because the black helps to absorb the UV light and stabilize the product. The best condition would be to store the components in a low light area or in a dark container.

As you can see, there are a lot of items that can affect shelf life of a rubber component. To set a general rule would be extremely difficult to do as every storage condition is different. You will have to make the decision by the appearance of the rubber component, or test the component in an actual application to determine if the components are still usable.

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